Loans - Summary of TDR and Related Credit Loss Reserves for TDR Loans - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Receivables [Abstract]
Other loans included in impaired loans apart from TDR loans	$ 79	$ 85
Residential Mortgage Loan TDR Carried At Lower Of Amortized Cost Or Fair Value Less Cost To Sell	778	763	718
Non Accrual loans included in TDR loan	$ 451	$ 485